The present invention relates to a method for judging a particle agglutination pattern formed on an inclined bottom surface of a reaction vessel by particles descending upon the bottom surface.
There has been proposed in, for instance, Japanese Patent Application Laid-open Publication No. 2,564/81, a method for judging a particle agglutination pattern formed on an inclined conical bottom surface of a reaction vessel by projecting images of central and peripheral portions of the bottom, onto first and second light receiving elements, respectively and by suitably processing outputs of the light receiving elements. In the case of using the reaction vessel having the conical bottom, when the agglutination reaction occurs between the particles in a reaction liquid contained in the vessel, the particles are agglutinated with each other and are uniformly deposited on the inclined bottom surface like snow to form a so-called uniform deposition pattern, whilst when the non-agglutination reaction occurs, the particles descending on the bottom roll down along the inclined bottom surface and are collected at the bottom center to form a so-called integral pattern. Now it is assumed that the output of the first light receiving element receiving the image of the central bottom portion is E.sub.1 and that of the second light receiving element receiving the image of the peripheral bottom portion is E.sub.2. Then, a difference .DELTA. E=.vertline.E.sub.2 -E.sub.1 .vertline. between these outputs E.sub.1 and E.sub.2 changes in accordance with the particle agglutination pattern. That is to say, when the particles descending upon the bottom surface form the clear uniform deposition pattern illustrated in FIGS. 1A and 1B and having a distribution of the particle amount shown in FIG. 1C, the difference .DELTA.E becomes extremely small. Contrary to this, when the clear integration pattern shown in FIGS. 2A, 2B and 2C is formed, the difference .DELTA.E becomes large. Therefore, by comparing the difference .DELTA.E with two reference values V.sub.1 and V.sub.2 (V.sub.1 &gt;V.sub.2) which can be obtained experimentally, it is possible to judge the agglutination reaction in such a manner that if .DELTA.E&lt;V.sub.2 (FIG. 1), the pattern is determined as the "agglutination pattern (+)", but if .DELTA.E&gt;V.sub.1 (FIG. 2), the pattern is judged to be the "non-agglutination pattern (-)". Furthermore, when the particle pattern has an intermediate agglutination as shown in FIGS. 3A, 3B and 3C, V.sub.2 .ltoreq..DELTA.E.ltoreq.V.sub.1 is obtained and in such a case the pattern can be judged as an "intermediate pattern (?)". If a sample is judged to be the intermediate pattern (?), the sample is tested again so to improve the reliability of analysis.
However, the above explained known judging method has the following drawbacks. When the amount of particles contained in the reaction liquid is small, the integral pattern (-) has the configuration illustrated in FIGS. 4A and 4B and the particle amount distribution depicted in FIG. 4C. In such a case, the difference .DELTA.E becomes small, because the number of the particles collected at the center of bottom is small. Then, .DELTA.E.ltoreq.V.sub.1 and the pattern is erroneously determined as the intermediate pattern (?), and in an extreme case, the integral pattern might be judged as the uniform deposition pattern (+). Moreover, when the number of particles in the reaction liquid is too large, even in case of the agglutination reaction, many particles which could not be agglutinated roll down along the uniformly deposited particle layer and are collected at the center to form a particle pattern shown in FIGS. 5A, 5B and 5C. Then, the difference .DELTA.E becomes larger than V.sub.2 or V.sub.1 and the pattern might be erroneously determined to be the intermediate patern (?) or the integral pattern (-) instead of the uniform deposition pattern (+).
Furthermore, as shown in FIGS. 6A, 6B and 6C, when the number of particles in the reaction liquid is too large and an unclear agglutination pattern is formed near the center portion due to a weak agglutination reaction, the agglutination pattern might be judged as the "integral pattern (-)" instead of the "intermediate pattern (?)", because .DELTA.E becomes equal to that of the particle pattern shown in FIG. 2. Therefore, there occurs a drawback that a little particle agglutination reaction near the center portion is likely to be overlooked.